Dynamics of the heart rate variability and oxygen saturation response to acute normobaric hypoxia within the first 10 min of exposure

Although the heart rate variability (HRV) response to hypoxia has been studied, little is known about the dynamics of HRV after hypoxia exposure. The purpose of this study was to assess the HRV and oxygen saturation (SpO₂) responses to normobaric hypoxia (FiO₂ = 9·6%) comparing 1 min segments to baseline (normoxia). Electrocardiogram and SpO₂ were recorded during a 10‐min hypoxia exposure in 29 healthy male subjects aged 26·0 ± 4·9 years. Baseline HRV values were obtained from a 5‐min recording period prior to hypoxia. The hypoxia period was split into 10 non‐overlapping 1‐min segments and time domain HRV indexes (RMSSD and SDNN) were calculated for each segment. Differences (Δ) from baseline values were calculated and transformed using natural logarithm (Ln). This study revealed that the decrease in ΔSpO₂ became significant (P<0·001) in the first minute of hypoxia, the decrease in ΔLn RMSSD became significant (P = 0·002) in the second minute, and the decrease in ΔLn SDNN became significant (P = 0·001) in the third minute. Between the second and fifth minute of hypoxia, ΔSpO₂ correlated with ΔLn RMSSD (r = 0·57, P<0·001) and ΔLn SDNN (r = 0·44, P<0·001). Five min after the onset of hypoxia, ΔSpO₂ was significantly (P = 0·002) decreased but changes in ΔLn RMSSD (P = 0·344) and ΔLn SDNN (P = 0·558) were not significant. In conclusion, the decrease in HRV was proportional to desaturation but only during the first 5 min of hypoxia.     

Acute resistance exercise with blood flow restriction effects on heart rate,double product,oxygen saturation and perceived exertion

The aim of this study was to compare the acute effect of resistance exercise (RE) with and without blood flow restriction (BFR) on heart rate (HR), double product (DP), oxygen saturation (SpO₂) and rating of perceived exertion (RPE). Twenty‐four men (21·79 ± 3·21 years) performed three experimental protocols in a random order (crossover): (i) high‐intensity RE at 80% of 1RM (HI), (ii) low‐intensity RE at 20% of 1RM (LI) and (iii) low‐intensity RE at 20% of 1RM combined with partial blood flow restriction (LI+BFR). HR, blood pressure, SpO₂ and RPE were assessed. The data were analysed using repeated measures analysis of variance and the Wilcoxon test for RPE. The results indicated that all protocols significantly increased HR, both immediately postexercise and during the subsequent 60 min (P<0·05), and postexercise DP (P<0·05), but there were no differences between protocols. The protocols of LI and LI+BFR reduced postexercise SpO₂ (P = 0·033, P = 0·007), and the LI+BFR protocol presented a perception of greater exertion in the lower limbs compared with HI (P = 0·022). We conclude that RE performed at low intensity combined with BFR seems to reduce the SpO₂ after exercise and increase HR and DP while maintaining a perception of greater exertion on the lower limbs.     

Influence of long-term oxygen therapy on cardiac acceleration and deceleration capacity in hypoxic patients with chronic obstructive pulmonary disease

Background: There is increasing interest in cardiovascular co‐morbidities of chronic obstructive pulmonary disease (COPD). Heart rate turbulence (HRT) and phase‐rectified signal averaging (PRSA) techniques quantify the heart’s acceleration/deceleration capacities. We postulated that these methods can help assess the integrity of cardiac control in hypoxic COPD. Methods: Eight hypoxic stable COPD patients, nine healthy age‐matched older adults and eight healthy young adults underwent ECG monitoring for 24 h. Patients with COPD were also monitored following 4 weeks of standardized oxygen therapy. HRT measures [turbulence onset (TO), turbulence slope (TS)] and PRSA‐derived acceleration/deceleration (AC, DC) indices were quantified within 6‐h blocks to assess circadian variation. Results: There were between‐group differences for variables TS, DC and AC (P<0·0005, η² = 0·54–0·65), attributable solely to differences between healthy young and COPD subjects. Only HR (P<0·0005) and DC index (P = 0·008) showed circadian variation. A significant interaction ‘trend’ effect for HR (F_9,87 = 2·52, P = 0·015, η² = 0·21) reflected the strong influence of COPD on HR circadian variation (afternoon and night values being different to those in healthy subjects). Conclusions: As expected, heart rate dynamics were substantially diminished in older (healthy and COPD) groups compared with healthy young controls. Patients with COPD showed similar heart rate dynamics compared with age‐matched controls, both before and after hypoxia correction. However, there was a suggestion of diminished DC in COPD compared with age‐matched controls (P = 0·059) that was absent following oxygen therapy. TS, DC and AC indices were altered by similar degrees in older subjects, apparently indicating equivalent tonic dysfunction of sympathetic/parasympathetic systems with ageing.     

Perfusion heterogeneity does not explain excess muscle oxygen uptake during variable intensity exercise

The association between muscle oxygen uptake (VO₂) and perfusion or perfusion heterogeneity (relative dispersion, RD) was studied in eight healthy male subjects during intermittent isometric (1 s on, 2 s off) one‐legged knee‐extension exercise at variable intensities using positron emission tomography and a‐v blood sampling. Resistance during the first 6 min of exercise was 50% of maximal isometric voluntary contraction force (MVC) (HI‐1), followed by 6 min at 10% MVC (LOW) and finishing with 6 min at 50% MVC (HI‐2). Muscle perfusion and O₂ delivery during HI‐1 (26 ± 5 and 5·4 ± 1·0 ml 100 g^?1 min^?1) and HI‐2 (28 ± 4 and 5·8 ± 0·7 ml 100 g^?1 min^?1) were similar, but both were higher (P<0·01) than during LOW (15 ± 3 and 3·0 ± 0·6 ml 100 g^?1 min^?1). Muscle VO₂ was also higher during both HI workloads (HI‐1 3·3 ± 0·4 and HI‐2 4·1 ± 0·6 ml 100 g^?1 min^?1) than LOW (1·4 ± 0·4 ml 100 g^?1 min^?1; P<0·01) and 25% higher during HI‐2 than HI‐1 (P<0·05). O₂ extraction was higher during HI workloads (HI‐1 62 ± 7 and HI‐2 70 ± 7%) than LOW (45 ± 8%; P<0·01). O₂ extraction tended to be higher (P = 0·08) during HI‐2 when compared to HI‐1. Perfusion was less heterogeneous (P<0·05) during HI workloads when compared to LOW with no difference between HI workloads. Thus, during one‐legged knee‐extension exercise at variable intensities, skeletal muscle perfusion and O₂ delivery are unchanged between high‐intensity workloads, whereas muscle VO₂ is increased during the second high‐intensity workload. Perfusion heterogeneity cannot explain this discrepancy between O₂ delivery and uptake. We propose that the excess muscle VO₂ during the second high‐intensity workload is derived from working muscle cells.     

Effect of exercise training and detraining on gas exchange kinetics in patients with chronic obstructive pulmonary disease

Symptom-limited incremental exercise tests are used to estimate the training effect on patients with chronic obstructive pulmonary disease (COPD). However, there is a need for objective parameters for measurement on submaximal exercise testing. The purpose of this study was to assess the usefulness of measurement of oxygen uptake (V?O₂) kinetics during a constant work rate exercise test of patients with COPD after exercise training. Eleven patients with COPD performed exercise tests before and after cycle ergometer training on 3 days per week for 8 weeks; they then went without training for 5 months and performed the same tests. They performed an incremental exercise test to symptom-limited maximum and a constant work rate exercise test for 6 min on a cycle ergometer. The time constant of V?O₂ during the onset of constant work rate exercise was significantly decreased (from 63·5±7·8 s to 53·2±8·0 s) after exercise training (P=0·021), but was significantly increased (to 73·4±14·9 s) after 5 months without training (P=0·001). The oxygen pulse at steady state during constant work rate exercise testing was significantly increased after exercise training but decreased 5 months later. The change in blood lactate from rest to steady state during constant work rate exercise was significantly decreased after exercise training, but increased 5 months later. Measurement of the time constant of V?O₂ and oxygen pulse during constant work rate exercise are useful for the objective evaluation of the training effect of patients with COPD.     

Commonly used reference values underestimate oxygen uptake in healthy, 50‐year‐old Swedish women

Cardiopulmonary exercise testing (CPET) is the gold standard among clinical exercise tests. It combines a conventional stress test with measurement of oxygen uptake (V_O2) and CO₂ production. No validated Swedish reference values exist, and reference values in women are generally understudied. Moreover, the importance of achieved respiratory exchange ratio (RER) and the significance of breathing reserve (BR) at peak exercise in healthy individuals are poorly understood. We compared V_O2 at maximal load (peakV_O2) and anaerobic threshold (V_O2@AT) in healthy Swedish individuals with commonly used reference values, taking gender into account. Further, we analysed maximal workload and peakV_O2 with regard to peak RER and BR. In all, 181 healthy, 50‐year‐old individuals (91 women) performed CPET. PeakV_O2 was best predicted using Jones et al. (100·5%). Furthermore, underestimation of peakV_O2 in women was found for all studied reference values (P<0·001) and was largest for Hansen‐Wasserman: women had 115% of predicted peakV_O2, while men had 103%. PeakV_O2 was similar in subjects with peak RER of 1–1·1 and RER > 1·1 (2 328·7 versus 2 176·7 ml min^?1, P = 0·11). Lower BR (≤30%) related to significantly higher peakV_O2 (P<0·001). In conclusion, peakV_O2 was best predicted by Jones. All studied reference values underestimated oxygen uptake in women. No evidence for demanding RER > 1·1 in healthy individuals was found. A lowered BR is probably a normal response to higher workloads in healthy individuals.     

Maintained cerebral metabolic ratio during exercise in patients with β‐adrenergic blockade

Background: Decreased cerebral metabolic ratio (CMR) [molar uptake of O₂ versus molar uptake of (glucose + ½ lactate)] during exercise is attenuated by intravenous administration of the non‐selective β‐adrenergic receptor antagonist propranolol. We evaluated to what extent cirrhotic patients in oral treatment with propranolol are able to mobilize brain non‐oxidative carbohydrate metabolism. Methods: Incremental cycle ergometry to exhaustion (86 ± 4·2 W; mean ± SD) was performed in eight cirrhotic patients instrumented with a catheter in the brachial artery and one retrograde in the right internal jugular vein. Healthy subjects form the control group. Results: In β‐blocked cirrhotic patients arterial lactate increased from 1·5 ± 0·3 to 5·1 ± 0·8 mM (P<0·05) and the arterial–jugular venous difference (a–v diff) from ?0·01 ± 0·03 to 0·30 ± 0·05 mM (P<0·05) at rest and during exercise, respectively. During exercise the glucose a–v diff of 0·46 ± 0·06 mM remained at a level similar to rest (0·54 ± 0·03 mM) and at exhaustion the CMR was not significantly changed (5·8 ± 1·1 versus 6·0 ± 0·6). In controls, CMR decreased from 5·6 ± 0·9 at rest to 3·4 ± 0·7 (P<0·05) during maximal exercise and at a lactate level comparable to that achieved by the patients it was 3·8 ± 0·4. Conclusion: During exhaustive exercise in cirrhotic patients the CMR is maintained and a significant cerebral uptake of lactate is demonstrated. The data suggest that oral treatment with a non‐selective β‐adrenergic receptor antagonist attenuates cerebral non‐oxidative metabolism.     

A programme based on repeated hypoxia–hyperoxia exposure and light exercise enhances performance in athletes with overtraining syndrome: a pilot study

Overtraining syndrome (OTS) is a major concern among endurance athletes and is a leading cause in preventing them to perform for long periods. Intermittent exposure to hypoxia has been shown to be an effective way of improving performance without exercising. Aim of this pilot study was to evaluate intermittent hypoxia–hyperoxia training combined with light exercise as an intervention to facilitate athletes with OTS to restore their usual performance level. Thirty-four track and field athletes were recruited: 15 athletes with OTS volunteered to participate and undertook a conditioning programme consisting of repeated exposures to hypoxia (O₂ at 10%) and hyperoxia (O₂ at 30%) (6–8 cycles, total time 45 min–1 h), three times a week, delivered 1·5–2 h after a low-intensity exercise session (2 bouts of 30 min, running at 50% of VO_2max with 10 min rest between bouts) over 4 weeks. Nineteen healthy track and field athletes volunteered to participate as a control group and followed their usual training schedule. Measurements before and after the intervention included exercise capacity, analysis of heart rate variability and hematological parameters. In athletes with OTS, a 4-week light exercise combined with intermittent hypoxia–hyperoxia training improved exercise performance (191·9 ± 26·9 W versus 170·8 ± 44·8 W in exercise capacity test, P = 0·01). Heart rate variability analysis revealed an improved sympatho-parasympathetic index (low frequency/high frequency ratio, 8·01 ± 7·51 before and 1·45 ± 1·71 after, P = 0·007). Hematological parameters were unchanged. Our pilot study showed that intermittent hypoxia–hyperoxia training and low-intensity exercise can facilitate functional recovery among athletes with OTS in a relatively short time.     

Calculation algorithms alter the breath‐by‐breath gas exchange values when abrupt changes in ventilation occur

The automatic metabolic units calculate breath‐by‐breath gas exchange from the expiratory data only, applying an algorithm (‘expiration‐only’ algorithm) that neglects the changes in the lung gas stores. These last are theoretically taken into account by a recently proposed algorithm, based on an alternative view of the respiratory cycle (‘alternative respiratory cycle’ algorithm). The performance of the two algorithms was investigated where changes in the lung gas stores were induced by abrupt increases in ventilation above the physiological demand. Oxygen, carbon dioxide fractions and ventilatory flow were recorded at the mouth in 15 healthy subjects during quiet breathing and during 20‐s hyperventilation manoeuvres performed at 5‐min intervals in resting conditions. Oxygen uptakes and carbon dioxide exhalations were calculated throughout the acquisition periods by the two algorithms. Average ventilation amounted to 6·1 ± 1·4 l min^?1 during quiet breathing and increased to 41·8 ± 27·2 l min^?1 during the manoeuvres (P<0·01). During quiet breathing, the two algorithms provided overlapping gas exchange data and noise. Conversely, during hyperventilation, the ‘alternative respiratory cycle’ algorithm provided significantly lower gas exchange data as compared to the values yielded by the ‘expiration‐only’ algorithm. For the first breath of hyperventilation, the average values provided by the two algorithms amounted to 0·37 ± 0·34 l min^?1 versus 0·96 ± 0·73 l min^?1 for O₂ uptake and 0·45 ± 0·36 l min^?1 versus 0·80 ± 0·58 l min^?1 for exhaled CO₂ (P<0·001 for both). When abrupt increases in ventilation occurred, such as those arising from a deep breath, the ‘alternative respiratory cycle’ algorithm was able to halve the artefactual gas exchange values as compared to the ‘expiration‐only’ approach.     

Influence of long‐term oxygen therapy on heart rate and QT time‐series in hypoxic patients with chronic obstructive pulmonary disease

Background: There is increasing interest in the cardiovascular pathology independently associated with chronic obstructive pulmonary disease (COPD). We examined the influence of long‐term oxygen therapy (LTOT) on heart rate (RR) and QT time‐series in COPD. Methods: Ten hypoxic stable COPD patients underwent Holter ECG monitoring for 24 h and physical activity/energy expenditure monitoring for 5 days before and after LTOT. Variability of RR and QT time‐series was quantified using standard statistics and their structural (correlation/scaling) properties were assessed using multifractal analysis. Pre‐ and post‐LTOT cardiac/activity parameters were compared to examine the influence of oxygen therapy and circadian variation. Results: PaO₂ increased (P = 0·0004) whilst PaCO₂ was unchanged (P = 0·56) following LTOT. Activity/energy expenditure estimates were also unchanged following LTOT (P = 0·64–0·99), but RR variability was increased during the morning (P < 0·05) and night (P < 0·1, trend only). Multifractality of RR and QT time‐series was not significantly changed following LTOT, although QT multifractality showed some time‐dependent fluctuations. Trends in RR and QT time‐series over 24‐h were similar pre‐ and post‐LTOT, indicating a generally normal circadian response. Conclusions: An increase in HRV following LTOT (but notably in the absence of altered activity levels) provides tentative evidence that LTOT has a direct effect on heart rate control in COPD. This beneficial influence was expressed mainly during the morning, and the relevance of this diurnal variation in response requires further investigation. It was also confirmed that both RR and (to a lesser degree) QT time‐series in COPD have a multifractal structure, and this is not affected appreciably by LTOT.     

Acute physiological and perceptual responses to high‐load resistance exercise in hypoxia

This study assessed whether hypoxia during high‐load resistance exercise could enhance the acute physiological responses related to muscular development. Twelve trained men performed exercise in three conditions: normoxia (fraction of inspired oxygen [F_IO₂] = 21%), moderate‐level hypoxia (F_IO₂ = 16%) and high‐level hypoxia (F_IO₂ = 13%). Exercise comprised high‐load squats and deadlifts (5 × 5 using 80% of 1‐repetition maximum with 180‐s rest). Muscle oxygenation and activation were monitored during exercise. Metabolic stress was estimated via capillary blood sampling. Perceived fatigue and soreness were also quantified following exercise. While the hypoxic conditions appeared to affect muscle oxygenation, significant differences between conditions were only noted for maximal deoxyhaemoglobin in the deadlift (P = 0·009). Blood lactate concentration increased from 1·1 to 1·2 mmol l^?1 at baseline to 9·5–9·8 mmol l^?1 after squats and 10·4–10·5 mmol l^?1 after deadlifts (P≤0·001), although there were no between‐condition differences. Perceived fatigue and muscle soreness were significantly elevated immediately and at 24 h following exercise, respectively, by similar magnitudes in all conditions (P≤0·001). Muscle activation did not differ between conditions. While metabolic stress is thought to moderate muscle activation and subsequent muscular development during hypoxic resistance training, it is not augmented during traditional high‐load exercise. This may be explained by the low number of repetitions performed and the long interset rest periods employed during this training. These findings suggest that high‐load resistance training might not benefit from additional hypoxia as has been shown for low‐ and moderate‐load training.     

Influence of work rate on the determinants of oxygen deficit during short-term submaximal exercise: implications for clinical research

Objective: The effect of increasing work rate was studied on the determinants of the oxygen deficit. Methods: Exercise testing was performed on a treadmill and gas exchange was measured on a breath‐by‐breath basis. Eleven healthy subjects, aged 18–25 years, performed three square wave exercise tests of different intensity. Before exercise, gas exchange was measured at rest in the standing position for 3 min, followed by a 6‐min square wave exercise test, randomly assigned at 4, 8 or 12% inclination. Immediately after exercise the recovery gas exchange was determined for 3 min. To calculate oxygen deficit, the oxygen uptake (O₂) values at onset of exercise were subtracted from the steady‐state value, the differences were cumulated and expressed as a percentage of the total oxygen cost for the 6‐min exercise. Results: The oxygen deficit increased significantly (P<0·001) with increasing work rate (6·1 ± 1·4% for 4%, 8·4 ± 2·1% for 8% and 9·4 ± 1·7% at 12% inclination). This resulted from a somewhat slower increase of O₂ at the onset of exercise at the highest work rate, reflected by a significantly higher time constant for O₂ at 8 and 12% (24·6 ± 7·3 s at 8% and 24·1 ± 6·3 s at 12% versus 20·2 ± 8·1 s at 4%). More importantly a significantly higher steady‐state value for O₂ was found at the highest exercise level, compared with the other exercise intensities. Conclusion: The higher oxygen deficit at the highest level of exercise is determined by a slower time constant and a higher asymptote value for O₂.     

Excessive exercise ventilation in moderate left heart dysfunction. Influence of postural changes in central haemodynamics and blood gases

To evaluate the relative importance of pulmonary congestion and peripheral hypoxia as causes for the excessive exercise ventilation in left heart dysfunction, seven patients with excessive ventilation and distinct left heart dysfunction during moderate exercise (LHD), and seven control patients with essentially normal exertional functions (CTR), had ventilation, central haemodynamics, arterial and mixed venous blood gases examined at rest and exercise, 32 W (25–40) in the LHD group and 44 W (33–49) in the CTR group, in lying and sitting positions. Change from lying to sitting exercise, led to fall in pulmonary artery wedge pressure (PAWP) from 31·0 ± 5·5 to 8·8 ± 5·0 mmHg in the LHD group, compared with from 13·7 ± 1·0 to 2·1 ± 2·4 mmHg in the controls, while ventilation/O₂ intake ratio (V˙/V˙O₂) and physiological dead space/tidal volume ratio (V_D/V_T) showed a tendency to rise, from 36·3 ± 8·8 to 39·2 ± 7·4, and from 0·35 ± 0·11 to 0·39 ± 0·09, respectively, in the LHD group, and from 27·5 ± 3·1 to 28·7 ± 5·3, and from 0·19 ± 0·09 to 0·21 ± 0·12 in the controls. Mixed venous O₂ tension (PvO ₂) showed a marked decline from 3·60 ± 0·33 to 3·26 ± 0·36 kPa in the LHD group, as compared with from 3·94 ± 0·28 to 3·71 ± 0·29 kPa in the controls, while the calculated physiologic shunt (Q˙_s/Q˙_t) suggested improved alveolo‐arterial gas exchange. The data fit in with recent studies ascribing the excessive exercise ventilation to a combination of signals from hypoxia‐induced changes, particularly in the exercising muscles, and augmented ergoreflex and central and peripheral chemoreceptor activity, partly to changes in the integrated control of ventilation and circulation, not to mechanisms related to pulmonary congestion.     

Use of non‐conventional nurses’ attire in a paediatric hospital: a quasi‐experimental study

Aims:  To test the impact of a multi‐coloured non‐conventional attire on a population of children admitted to a paediatric hospital. Design:  Quasi‐experimental before‐after controlled study. Background:  It has been suggested that non‐conventional nurses’ uniforms in paediatric settings may contribute to lowering children’s distrust towards healthcare providers and reduce fear. Little formal research has investigated on the impact of nursing attire in a paediatric setting. No study has so far analysed the effects in actual use of a non‐conventional, other than the traditional type of uniform, on a paediatric hospitalised population. Design:  A quasi‐experimental study. Methods:  We introduced multi‐coloured nurses’ attire in two wards of a paediatric hospital. Using open questions and semantic differential scales (SDS), we evaluated the effects of this non‐conventional attire on a group of hospitalised children, compared to sex‐and‐age‐matched controls interviewed before the introduction. Parents were also interviewed. Results:  One hundred and twelve hospitalised children and their parents (n = 112) were studied. The percentage of positive words used by children to define their nurse was higher in children interviewed after the introduction of non‐conventional uniforms (96·2% vs. 81·8%, p = 0·01). Children’s perception of nurses was significantly improved by the use of multi‐coloured attire (‘bad’–‘good’ SDS: p = 0·01; ‘disagreeable’–‘nice’ SDS: p = 0·001). Children’s perceptions regarding hospital environment did not change. Parents’ perception of nurses’ uniform adequacy to the role and capability to reassure resulted improved (p < 0·0001, p = 0·0003). Conclusions:  Multi‐coloured non‐conventional attire were preferred by hospitalised children and their parents. Their introduction improved the perception children have of their nurses. Moreover, the coloured uniforms improve the parents perception about the reliability of the nurse. Relevance to clinical practice:  The use of non‐conventional nurses’ attire can contribute to improve the child–nurse relation, which has the potential to ease the discomfort experienced by children due to hospitalisation.     

Transcutaneous versus arterial oxygen tension during exercise in chronic pulmonary disease

Summary. Simultaneous transcutaneous (P_tc O₂) and arterial (P_a O₂) oxygen tension measurements were obtained at rest and during exercise in 15 subjects with known or suspected chronic lung disease. The overall correlation coefficient between P_tc O₂ and P_a O₂ was 0·74, and the mean difference between the two variables was — 1·9kPa (14 mmHg). The correlation coefficient was somewhat, but not significantly, higher during exercise (r=0·86) than at rest (r=0·58). Large random discrepancies between simultaneous observations of P_tc O₂ and P_a O₂ as well as between changes in P_tc O₂ and changes in P_a O₂ in individual subjects were observed. It is concluded that P_tc O₂ cannot be substituted for P_a O₂ in exercise testing applied in the diagnosis and assessment of lung disease.     

Intensity of Nordic Walking in young females with different peak O2 consumption

The purpose of this cross‐sectional study was to determine the physiological reaction to the different intensity Nordic Walking exercise in young females with different aerobic capacity values. Twenty‐eight 19–24‐year‐old female university students participated in the study. Their peak O₂ consumption (VO₂ peak kg^?1) and individual ventilatory threshold (IVT) were measured using a continuous incremental protocol until volitional exhaustion on treadmill. The subjects were analysed as a whole group (n = 28) and were also divided into three groups based on the measured VO₂ peak kg^?1 (Difference between groups is 1 SD) as follows: 1. >46 ml min^?1 kg^?1 (n = 8), 2. 41–46 ml min^?1 kg^?1 (n = 12) and 3. <41 ml min^?1 kg^?1 (n = 8). The second test consisted of four times 1 km Nordic Walking with increasing speed on the 200 m indoor track, performed as a continuous study (Step 1 – slow walking, Step 2 – usual speed walking, Step 3 – faster speed walking and Step 4 – maximal speed walking). During the walking test expired gas was sampled breath‐by‐breath and heart rate (HR) was recorded continuously. Ratings of perceived exertion (RPE) were asked using the Borg RPE scale separately for every 1 km of the walking test. No significant differences emerged between groups in HR of IVT (172·4 ± 10·3–176·4 ± 4·9 beats min^?1) or maximal HR (190·1 ± 7·3–191·6 ± 7·8 beats min^?1) during the treadmill test. During maximal speed walking the speed (7·4 ± 0·4–7·5 ± 0·6 km h^?1) and O₂ consumption (30·4 ± 3·9–34·0 ± 4·5 ml min^?1 kg^?1) were relatively similar between groups (P > 0·05). However, during maximal speed walking, the O₂ consumption in the second and third groups was similar with the IVT (94·9 ± 17·5% and 99·4 ± 15·5%, respectively) but in the first group it was only 75·5 ± 8·0% from IVT. Mean HR during the maximal speed walking was in the first group 151·6 ± 12·5 beats min^?1, in the second (169·7 ± 10·3 beats min^?1) and the third (173·1 ± 15·8 beats min^?1) groups it was comparable with the calculated IVT level. The Borg RPE was very low in every group (11·9 ± 2·0–14·4 ± 2·3) and the relationship with VO₂and HR was not significant during maximal speed Nordic Walking. In summary, the present study indicated that walking is an acceptable exercise for young females independent of their initial VO₂ peak level. However, females with low initial VO₂ peak can be recommended to exercise with the subjective ‘faster speed walking’. In contrast, females with high initial VO₂ peak should exercise with maximal speed.     

Functional near‐infrared spectroscopy to probe sensorimotor region activation during electrical stimulation‐evoked movement

This study used non‐invasive functional near‐infrared spectroscopy (fNIRS) neuroimaging to monitor bilateral sensorimotor region activation during unilateral voluntary (VOL) and neuromuscular electrical stimulation (NMES)‐evoked movements. Methods. In eight healthy male volunteers, fNIRS was used to measure relative changes in oxyhaemoglobin (O₂Hb) and deoxyhaemoglobin (HHb) concentrations from a cortical sensorimotor region of interest in the left (LH) and right (RH) hemispheres during NMES‐evoked and VOL wrist extension movements of the right arm. Results. NMES‐evoked movements induced significantly greater activation (increase in O₂Hb and concomitant decrease in HHb) in the contralateral LH than in the ipsilateral RH (O₂Hb: 0·44 ± 0·16 μM and 0·25 ± 0·22 μM, P = 0·017; HHb: ?0·19 ± 0·10 μM and ?0·12 ± 0·09 μM, P = 0·036, respectively) as did VOL movements (0·51 ± 0·24 μΜ and 0·34 ± 0·21 μM, P = 0·031; HHb: ?0·18 ± 0·07 μΜ and ?0·12 ± 0·04 μΜ, P = 0·05, respectively). There was no significant difference between conditions for O₂Hb (P = 0·144) and HHb (P = 0·958). Conclusion. fNIRS neuroimaging enables quantification of bilateral sensorimotor regional activation profiles during voluntary and NMES‐evoked wrist extension movements.     

Non‐invasive measurement of cardiac output by Finometer in patients with cirrhosis

The Finometer measures haemodynamic parameters including cardiac output (CO) using non‐invasive volume‐clamp techniques. The aim of this study was to determine the accuracy of the Finometer in hyperdynamic cirrhotic patients using an invasive indicator dilution technique as control. CO was measured in twenty‐three patients referred for invasive measurements of the hepatic venous pressure gradient on suspicion of cirrhosis. Invasive measurements of CO were performed using indicator dilution technique (CO_I) and simultaneous measurements of CO were recorded with the Finometer (CO_F). In six patients, measurements of CO were performed with invasive technique and the Finometer both before and after β‐blockade using 80 mg of propranolol and the changes in CO (ΔCO_I and ΔCO_F respectively) were calculated to evaluate the Finometers ability to detect relative changes in CO. Mean CO_I was 6·1 ± 1·6 [3·9;9·7] l min^?1 (mean ± SD [range]) compared to mean CO_F of 7·2 ± 2·3 [3·1;11·9] l min^?1. There was a mean difference between CO_F and CO_I of 1·0 ± 1·8 [?2·1;4·0] l min^?1 and 95% confidence interval of [0·2;1·8], P<0·001. In patients with measurements before and after β‐blockade, mean ΔCO_I was 1·6 ± 1·4 [?0·1;3·3] l min^?1 compared to mean ΔCO_F of 1·9 ± 1·3 [0·4;3·8] l min^?1. Mean difference between ΔCO_F and ΔCO_I was 0·3 ± 0·3 [?0·2;0·7] l min^?1 with a 95% confidence interval of [?0·1;0·6], P = 0·11. Compared with invasive measurements, the Finometer can be used to measure changes in CO, whereas absolute measurements are associated with higher variation in patients with cirrhosis. The Finometer seems useful for repeated determinations such as in studies of effect of pharmacotherapy.     

Validity of Oxycon Mobile in measuring inspiratory capacity in healthy subjects

Introduction: Inspiratory capacity (IC) assessments have been performed mainly in laboratory settings, because of fixed measurement devices. Oxycon Mobile^® (OM) is the mobile and wireless version of Oxycon Pro^® (OP), a commonly used fixed measurement device. The purpose of this study was to examine IC agreement between OM and OP at rest and during steady‐state exercise. Also, the within‐ and between‐days variability of IC’s were determined. Methods: Thirty‐five healthy subjects were recruited. Twenty‐five subjects were included for determining validity of the OM and ten subjects for the variability study. For validation of OM, resting and exercise IC’s (IC_rest and IC_exercise respectively) were measured consecutively by OM and OP, in random order. Exercise consisted of cycle ergometry at 50% of subject’s predicted maximal exercise capacity. Results: The mean difference between OM and OP regarding IC_rest was ?0·05L, with limits of agreement of ?0·47 to 0·37L (or ?1·2% with limits of agreement of ?11·6 to 9·3%) (P>0·05). The mean difference of IC_exercise was ?0·06L, and the limits of agreement were ?0·48 to 0·35L (or ?1·4% with limits of agreement of ?11·8 to 9·0%) (P>0·05). No significant differences in IC’s within‐ or between‐days were found. Discussion: The limits of agreement of the IC measured by OM and OP were ±10%, which is recommended for interdevice reproducibility. We conclude that OM and OP can be used interchangeably for measuring IC at rest and during steady‐state exercise.